Network Working Group F. Templin Internet-Draft Nokia Expires:
September 25, 2003February 23, 2004 T. Gleeson Cisco Systems K.K. M. Talwar D. Thaler Microsoft Corporation March 27,August 25, 2003 Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) draft-ietf-ngtrans-isatap-13.txtdraft-ietf-ngtrans-isatap-14.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 25, 2003.February 23, 2004. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document specifies an Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) that connects IPv6 hosts and routers within IPv4 sites. ISATAP treats the site's IPv4 infrastructure as a link layer for IPv6 with no requirement for IPv4 multicast. ISATAP enables intra-site automatic IPv6-in-IPv4 tunneling whether globally assigned or private IPv4 addresses are used. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Applicability Statement . . . . . . . . . . . . . . . . . . . 3 3.Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3 4.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 5.3 4. Basic IPv6 Operation . . . . . . . . . . . . . . . . . . . . . 4 6.5. Automatic Tunneling . . . . . . . . . . . . . . . . . . . . . 5 7.6. Neighbor Discovery . . . . . . . . . . . . . . . . . . . . . . 6 8. Deployment7. IANA Considerations . . . . . . . . . . . . . . . . . . 9 9. Site Administration Considerations. . . 9 8. Security considerations . . . . . . . . . . . 9 10. IANA Considerations. . . . . . . . 9 9. Acknowledgements . . . . . . . . . . . . . 10 11. Security considerations. . . . . . . . . . 9 Normative References . . . . . . . . . 10 12. Acknowledgements. . . . . . . . . . . . 10 Informative References . . . . . . . . . . . 10 Normative References. . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . 11 Informative References. . . . . . . . . . 12 A. Major Changes . . . . . . . . . . 11 Authors' Addresses. . . . . . . . . . . . . . 12 B. Rationale for Interface Identifier Construction . . . . . . . 14 C. Deployment Considerations . 12 A. Major Changes. . . . . . . . . . . . . . . . . 15 D. Site Administration Considerations . . . . . . . 13 B. Rationale for Interface Identifier Construction. . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . 17 1. Introduction This document presents a simple approach called the Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) that enables incremental deployment of IPv6 [RFC2460] within IPv4 [RFC0791] sites. ISATAP allows dual-stack nodes that do not share a physical link with an IPv6 router to automatically tunnel packets to the IPv6 next-hop address through IPv4, i.e., the site's IPv4 infrastructure is treated as a link layer for IPv6. Specific details for the operation of IPv6 and automatic tunneling using ISATAP are given, including an interface identifier format that embeds an IPv4 address. This format supports IPv6 address configuration and simple link-layer address mapping. Also specified is the operation of IPv6 Neighbor Discovery and deployment/security considerations. 2. Applicability Statement ISATAP provides the following features: o treats site's IPv4 infrastructure as a link layer for IPv6 using automatic IPv6-in-IPv4 tunneling o enables incremental deployment of IPv6 hosts within IPv4 sites with no aggregation scaling issues at border gateways o requires no special IPv4 services within the site (e.g., multicast) o supports both stateless and stateful autoconfiguration as well as manual configuration o supports networks that use non-globally unique IPv4 addresses (e.g., when private address allocations [RFC1918] are used) o compatible with other NGTRANS mechanisms (e.g., 6to4 [RFC3056]) 3.Requirements The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [RFC2119]. This document also makes use of internal conceptual variables to describe protocol behavior and external variables that an implementation must allow system administrators to change. The specific variable names, how their values change, and how their settings influence protocol behavior are provided to demonstrate protocol behavior. An implementation is not required to have them in the exact form described here, so long as its external behavior is consistent with that described in this document. 4.3. Terminology The terminology of [RFC2460] applies to this document. The following additional terms are defined: link, on-link, off-link: same definitions as ([RFC2461], section 2.1). underlying link: a link layer that supports IPv4 (for ISATAP), and MAY also support IPv6 natively. ISATAP interface: an interface configured over one or more underling links. advertising ISATAP interface: same meaning as "advertising interface" in ([RFC2461], section 6.2.2). ISATAP address: an on-linkaddress with an on-link prefix on an ISATAP interface and with an interface identifier constructed as specified in Section 5.1 5.4.1 4. Basic IPv6 Operation ISATAP interfaces automatically tunnel IPv6 packets using the site's IPv4 infrastructure as a link layer for IPv6, i.e., IPv6 treats the site's IPv4 infrastructure as a Non-Broadcast, Multiple Access (NBMA) link layer. The mechanisms in [RFC2491] are used, with the following noted exceptions for ISATAP: 5.14.1 Interface Identifiers and Unicast Addresses ISATAP interface identifiers use "modified EUI-64" format ([ARCH],([RFC3513], section 2.5.1) and are formed by appending an IPv4 address assigned to an underlying link to the 32-bit string '00-00-5E-FE'. Appendix B includes non-normative rationale for this construction rule. IPv6 global and local-use ([ARCH],([RFC3513], sections 2.5.4, 2.5.6) ISATAP addresses are constructed as follows: | 64 bits | 32 bits | 32 bits | +------------------------------+---------------+----------------+ | global/local unicast prefix | 0000:5EFE | IPv4 Address | +------------------------------+---------------+----------------+ 5.24.2 ISATAP Interface Configuration ISATAP interfaces are configured over one or more underlying links that support IPv4 for tunneling within a site; each IPv4 address assigned to an underlying link is seen as a link-layer address for ISATAP. 5.34.3 Link Layer Address Options With reference to ([RFC2491], section 5.2), when the [NTL] and [STL] fields in an ISATAP link layer address option encode 0, the [NBMA Number] field encodes a 4-octet IPv4 address. 5.44.4 Multicast and Anycast ISATAP interfaces recognize an IPv6 node's required addresses ([ARCH],([RFC3513], section 2.8), including certain multicast/anycast addresses. Mechanisms for multicast/anycast emulation on ISATAP interfaces (e.g., adaptations of MLD [RFC2710], PIM-SM [RFC2362], MARS [RFC2022], etc.) are subject for future companion document(s). 6.5. Automatic Tunneling The common tunneling mechanisms specified in ([MECH], sections 2 and 3) are used, with the following noted considerations for ISATAP: 6.15.1 Tunnel MTU and Fragmentation ISATAP automatic tunnel interfaces may be configured over multiple underlying links with diverse maximum transmission units (MTUs). The minimum MTU for IPv6 interfaces is 1280 bytes ([RFC2460], Section 5), but the following considerations apply for ISATAP interfaces: o Nearly all IPv4 nodes connect to physical links with MTUs of 1500 bytes or larger (e.g., Ethernet) o Sub-IPv4 layer encapsulations (e.g., VPN) may occur on some paths o Commonly-deployed VPN interfaces use an MTU of 1400 bytes To maximize efficiency and minimize IPv4 fragmentation for the predominant deployment case, the ISATAP interface MTU, or "LinkMTU" (see: [RFC2461], Section 6.3.2), SHOULD be set to no more than 1380 bytes (1400 minus 20 bytes for IPv4 encapsulation). LinkMTU MAY be set to larger values when a dynamic link layer MTU discovery mechanism is used or when a static MTU assignment is used and additional fragmentation in the site's IPv4 network is deemed acceptable. When a dynamic IPv4 MTU discovery mechanism is not used, the ISATAP interface encapsulates IPv6 packets with the Don't Fragment (DF) bit not set in the encapsualtingencapsulating IPv4 header. 6.25.2 Handling IPv4 ICMP Errors ARP failures and persistent ICMPv4 errors SHOULD be processed as link-specific information indicating that a path to a neighbor has failed ([RFC2461], section 7.3.3). 6.35.3 Local-Use IPv6 Unicast Addresses The specification in ([MECH], section 3.7) is not used; the specification in Section 5.14.1 is used instead. 7.6. Neighbor Discovery The specification in ([MECH], section 3.8) applies only to configured tunnels. [RFC2461] provides the following guidelines for non-broadcast multiple access (NBMA) link support: "Redirect, Neighbor Unreachability Detection and next-hop determination should be implemented as described in this document. Address resolution and the mechanism for delivering Router Solicitations and Advertisements on NBMA links is not specified in this document." ISATAP interfaces SHOULD implement Redirect, Neighbor Unreachability Detection, and next-hop determination exactly as specified in [RFC2461]. Address resolution and the mechanisms for delivering Router Solicitations and Advertisements are not specified by [RFC2461]; instead, they are specified in the following sections of this document. 7.16.1 Address Resolution and Neighbor Unreachability Detection ISATAP addresses are resolved to link-layer (IPv4) addresses by a static computation, i.e., the last four octets are treated as an IPv4 address. Hosts SHOULD perform an initial reachability confirmation by sending Neighbor Solicitation (NS) message(s) and receiving a Neighbor Advertisement (NA) message as specified in ([RFC2461], section 7.2). Unless otherwise specified in a future document, solicitations are sent to the target's unicast address. Hosts SHOULD additionally perform Neighbor Unreachability Detection (NUD) as specified in ([RFC2461], section 7.3). Routers MAY perform these reachability confirmation and NUD procedures, but this might not scale in all environments. All ISATAP nodes MUST send solicited neighbor advertisements ([RFC2461], section 7.2.4). 7.26.2 Duplicate Address Detection Duplicate Address Detection ([RFC2462], section 5.4) is not required for ISATAP addresses, since duplicate address detection is assumed already performed for the IPv4 addresses from which they derive. 7.36.3 Router and Prefix Discovery The following sections describe mechanisms to support the router and prefix discovery process ([RFC2461], section 6): 188.8.131.52.1 Conceptual Data Structures ISATAP nodes use the conceptual data structures Prefix List and Default Router List exactly as in ([RFC2461], section 5.1). ISATAP adds a new conceptual data structure "Potential Router List" (PRL) and the following new configuration variable: PrlRefreshInterval Time in seconds between successive refreshments of the PRL after initialization. SHOULD be no less than 3,600 seconds. Default: 3,600 seconds A PRL is associated with every ISATAP interface. Each entry in the PRL ("PRL(i)") has an IPv4 address ("V4ADDR(i)") that represents an advertising ISATAP interface and an associated timer ("TIMER(i)"). When a node enables an ISATAP interface, it initializes the PRL with IPv4 addresses. The addresses MAY be discovered via a DHCPv4 [RFC2131] option for ISATAP, manual configuration, or an unspecified alternate method (e.g., DHCPv4 vendor-specific option). When no other mechanisms are available, a DNS fully-qualified domain name (FQDN) [RFC1035] established by an out-of-band method (e.g., DHCPv4, manual configuration, etc.) MAY be used. The FQDN is resolved into IPv4 addresses for the PRL through a static host file, a site-specific name service, querying a DNS server within the site, or an unspecified alternate method. There are no mandatory rules for the selection of a FQDN, but manual configuration MUST be supported. When DNS is used, client resolvers use the IPv4 transport. After initialization, nodes periodically refresh the PRL (i.e., using one or more of the methods described above) after PrlRefreshInterval. 184.108.40.206.2 Validation of Router Advertisements Messages The specification in ([RFC2461], section 6.1.2) is used. Additionally, received RA messages that contain Prefix Information options and/or encode non-zero values in the Cur Hop Limit, Router Lifetime, Reachable Time, or Retrans Timer fields (see: [RFC2461], section 4.2) MUST satisfy the following validity check for ISATAP: o the network-layer (IPv6) source address is an ISATAP address and embeds V4ADDR(i) for some PRL(i) 220.127.116.11.3 Router Specification Routers with advertising ISATAP interfaces behave the same as described in ([RFC2461], section 6.2). As permitted by ([RFC2461], section 6.2.6), advertising ISATAP interfaces SHOULD send unicast RA messages to a soliciting host's unicast address when the solicitation's source address is not the unspecified address. 18.104.22.168.4 Host Specification Hosts behave the same as described in ([RFC2461], section 6.3) and ([RFC2462], section 5.5) with the following additional considerations for ISATAP: 22.214.171.124.3.4.1 Soliciting Router Advertisements Hosts solicit Router Advertisements (RAs) by sending Router Solicitations (RSs) to advertising ISATAP interfaces in the PRL. The manner of selecting PRL(i)'s for solicitation is up to the implementation. Hosts add the following variable to support the solicitation process: MinRouterSolicitInterval Minimum time in seconds between successive solicitations of the same advertising ISATAP interface. SHOULD be no less than 900 seconds. Default: 900 seconds RS messages use a link-local unicast address from the ISATAP interface as the IPv6 source address. Unless otherwise specified in a future document, RS messages use the link-local ISATAP address constructed from V4ADDR(i) for the PRL(i) being solicited as the IPv6 destination address. 126.96.36.199.3.4.2 Router Advertisement Processing RA processing is exactly as specified in ([RFC2461], section 6.3.4). Prefix options in RAs with the "L" bit not set contain prefixes that are not considered on-link with the ISATAP interface and MAY be used to configure non-ISATAP addresses, e.g., using [RFC2462] mechanisms. When the source address of an RA message is an ISATAP address that embeds V4ADDR(i) for some PRL(i), hosts reset TIMER(i) to schedule the next solicitation event (see: Section 188.8.131.52).184.108.40.206). Let "MIN_LIFETIME" be the minimum value in the router lifetime or the lifetime(s) encoded in options included in the RA message. Then, TIMER(i) is reset as follows: TIMER(i) = MAX((0.5 * MIN_LIFETIME), MinRouterSolicitInterval) 220.127.116.11.3.4.3 Stateful Autoconfiguration If stateful autoconfiguration is invoked ([RFC2462], sections 5.5.2, 5.5.3), the "ALL_DHCP_Relay_Agents_and_Servers""All_DHCP_Relay_Agents_and_Servers" multicast address ([DHCPV6],([RFC3315], section 5.1) is resolved to the link-local ISATAP address constructed fromV4ADDR(i) for some PRL(i). 8. Deployment Considerations Hosts may enable ISATAP, e.g., when native IPv6 service is unavailable. When native IPv6 service is acquired, hosts SHOULD discontinue the ISATAP router solicitation process (Section 7.3.4) and/or allow associated state to expire (see: [RFC2461], section 5.3 and [RFC2462], section 5.5.4). Any associated addresses added to the DNS should also be removed. Routers MAY configure both native IPv6 and ISATAP interfaces over the same physical link. The prefixes used on each interface will be distinct, and normal IPv6 routing between the interfaces may occur. 9. Site Administration Considerations ISATAP sites are administratively defined by a set of advertising interfaces and set of nodes that solicit those interfaces. Thus, ISATAP sites are defined by administrative (not physical) boundaries. Site administrators maintain a list of IPv4 addresses representing advertising ISATAP interfaces and make them available via one or more of the mechanisms described in Section 7.3.1. Responsible administration can reduce control traffic overhead. 10.7. IANA Considerations Modifications to the IANA "ethernet-numbers" registry (e.g., based on text in Appendix B) are requested. 11.8. Security considerations ISATAP site border routers and firewalls MUST implement IPv6 and IPv4 ingress filtering, including ip-protocol-41 filtering. Packets with local-use source and/or destination addresses MUST NOT be forwarded outside of the site. Even with IPv4 and IPv6 ingress filtering, reflection attacks can originate from compromised nodes within an ISATAP site that spoof IPv6 source addresses. Security mechanisms for reflection attack mitigation SHOULD be used in routers with advertising ISATAP interfaces. At a minimum, border gateways SHOULD log potential source address spoofing cases. ISATAP addresses do not support privacy extensions for stateless address autoconfiguration [RFC3041]. However, since the ISATAP interface identifier is derived from the node's IPv4 address, ISATAP addresses do not have the same level of privacy concerns as IPv6 addresses that use an interface identifier derived from the MAC address. (This is especially true when private address allocations [RFC1918] are used.) 12.9. Acknowledgements SomePortions of the ideas presented inthis draftwork were derived from work atSRI withInternational internal funds and contractual support.government contracts. Government sponsors who supported the workinclude Monica Farah-Stapleton and Russell Langan from U.S.(U.S. Army CECOM ASEO,ASEO), and Dr. Allen Moshfegh from U.S.(U.S. Office of Naval Research. Within SRI,Research). SRI International sponsors include Dr. Mike Frankel, J. Peter Marcotullio, Lou Rodriguez, and Dr. Ambatipudi Sastry supported the work and helped foster early interest.Sastry. The following peer reviewersare acknowledged for taking the time toproviding peer review a pre-release of this document and provideinput: Jim Bound, Rich Draves, Cyndi Jung, Ambatipudi Sastry, Aaron Schrader, Ole Troan, Vlad Yasevich. The authors acknowledge members of the NGTRANS community who have made significant contributions to this effort, includingfollowing additional individuals are acknowledged for their contributions: Rich Draves, Alain Durand, Nathan Lutchansky, Karen Nielsen, Mohan Parthasarathy, Art Shelest, Margaret Wasserman, andBrian Zill. The authors also wish toacknowledge the work of Quang Nguyen [VET] under the guidance of Dr. Lixia Zhang that proposed very similar ideas to those that appear in this document. This work was first brought to the authors' attention on September 20, 2002. Normative References [ARCH] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", draft-ietf-ipngwg-addr-arch-v3-11 (work in progress), October 2002.[MECH] Gilligan, R. and E. Nordmark, "Basic Transition Mechanisms for IPv6 Hosts and Routers", draft-ietf-v6ops-mech-v2-00 (work in progress), February 2003. [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. [RFC2463] Conta, A. and S. Deering, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 2463, December 1998. [RFC2491] Armitage, G., Schulter, P., Jork, M. and G. Harter, "IPv6 over Non-Broadcast Multiple Access (NBMA) networks", RFC 2491, January 1999. [RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6) Addressing Architecture", RFC 3513, April 2003. Informative References [DHCPV6] Droms, R., "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress), November 2002.[RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. [RFC1546] Partridge, C., Mendez, T. and W. Milliken, "Host Anycasting Service", RFC 1546, November 1993. [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G. and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996. [RFC2022] Armitage, G., "Support for Multicast over UNI 3.0/3.1 based ATM Networks", RFC 2022, November 1996. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC2185] Callon, R. and D. Haskin, "Routing Aspects Of IPv6 Transition", RFC 2185, September 1997. [RFC2362] Estrin, D., Farinacci, D., Helmy, A., Thaler, D., Deering, S., Handley, M. and V. Jacobson, "Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification", RFC 2362, June 1998. [RFC2710] Deering, S., Fenner, W. and B. Haberman, "Multicast Listener Discovery (MLD) for IPv6", RFC 2710, October 1999. [RFC3041] Narten, T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001. [RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via IPv4 Clouds", RFC 3056, February 2001. [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [VET] Nguyen, Q., "http://irl.cs.ucla.edu/vet/report.ps", spring 1998. Authors' Addresses Fred L. Templin Nokia 313 Fairchild Drive Mountain View, CA 94110 US Phone: +1 650 625 2331 EMail: email@example.com Tim Gleeson Cisco Systems K.K. Shinjuku Mitsu Building 2-1-1 Nishishinjuku, Shinjuku-ku Tokyo 163-0409 Japan EMail: firstname.lastname@example.org Mohit Talwar Microsoft Corporation One Microsoft Way Redmond, WA> 98052-6399 US Phone: +1 425 705 3131 EMail: email@example.com Dave Thaler Microsoft Corporation One Microsoft Way Redmond, WA 98052-6399 US Phone: +1 425 703 8835 EMail: firstname.lastname@example.org Appendix A. Major Changes changes from version 13 to version 14: o removed applicability statement; applicability TBD by v6ops o updated deployment/site admin sections; moved to appendices o new text on "L" bit in prefix options in section 18.104.22.168 o removed extraneous text in Security Considerations o fixed "layering bug" in section 22.214.171.124 o revised "ISATAP address" definition o updated references for RFC 3315; 3513 changes from version 12 to version 13: o Added comments from co-authors o Text cleanup; removed extraneous text o Revised ISATAP interface/link terminology o Returned to using symbolic reference names o Revised MTU section; moved non-normative MTU text to seperateseparate document changes from earlier versions to version 12: o Added multicast/anycast subsection o Revised PRL initialization o Updated neighbor discovery, security consideration sections o Rearranged/revised sections 5, 6, 7 o Added stateful autoconfiguration mechanism o Normative references to RFC 2491, RFC 2462 o Moved non-normative MTU text to appendix C o clarified address resolution, Neighbor Unreachability Detection o specified MTU/MRU requirements o Addressed operational issues identified in 05 based on discussion between co-authors o Clarified ambiguous text per comments from Hannu Flinck; Jason Goldschmidt o Moved historical text in section 4.1 to Appendix B in response to comments from Pekka Savola o Identified operational issues for anticipated deployment scenarios o Included reference to Quang Nguyen work Appendix B. Rationale for Interface Identifier Construction ISATAP specifies an EUI64-format address construction for the Organizationally-Unique Identifier (OUI) owned by the Internet Assigned Numbers Authority (IANA). This format (given below) is used to construct both native EUI64 addresses for general use and modified EUI-64 format interface identifiers for IPv6 unicast addresses: |0 2|2 3|3 3|4 6| |0 3|4 1|2 9|0 3| +------------------------+--------+--------+------------------------+ | OUI ("00-00-5E"+u+g) | TYPE | TSE | TSD | +------------------------+--------+--------+------------------------+ Where the fields are: OUI IANA's OUI: 00-00-5E with 'u' and 'g' bits (3 octets) TYPE Type field; specifies use of (TSE, TSD) (1 octet) TSE Type-Specific Extension (1 octet) TSD Type-Specific Data (3 octets) And the following interpretations are specified based on TYPE: TYPE (TSE, TSD) Interpretation ---- ------------------------- 0x00-0xFD RESERVED for future IANA use 0xFE (TSE, TSD) together contain an embedded IPv4 address 0xFF TSD is interpreted based on TSE as follows: TSE TSD Interpretation --- ------------------ 0x00-0xFD RESERVED for future IANA use 0xFE TSD contains 24-bit EUI-48 intf id 0xFF RESERVED by IEEE/RAC Thus, if TYPE=0xFE, TSE is an extension of TSD. If TYPE=0xFF, TSE is an extension of TYPE. Other values for TYPE (thus, other interpretations of TSE, TSD) are reserved for future IANA use. The above specification is compatible with all aspects of EUI64, including support for encapsulating legacy EUI-48 interface identifiers (e.g., an IANA EUI-48 format multicast address such as: '01-00-5E-01-02-03' is encapsulated as: '01-00-5E-FF-FE-01-02-03'). But, the specification also provides a special TYPE (0xFE) to indicate an IPv4 address is embedded. Thus, when the first four octets of an IPv6 interface identifier are: '00-00-5E-FE' (note: the 'u/l' bit MUST be 0) the interface identifier is said to be in "ISATAP format" and the next four octets embed an IPv4 address encoded in network byte order. Appendix C. Deployment Considerations Hosts can enable ISATAP, e.g., when native IPv6 service is unavailable. When native IPv6 service is acquired, hosts can discontinue the ISATAP router solicitation process (Section 6.3.4) and/or allow associated state to expire (see: [RFC2461], section 5.3 and [RFC2462], section 5.5.4). In this case, any associated addresses added to the DNS should also be removed. Routers can configure both native IPv6 and ISATAP interfaces over the same physical link. The prefixes used on each interface will be distinct, and normal IPv6 routing between the interfaces can occur. Routers can include prefix options with the "L" bit not set in RAs sent on ISATAP interfaces provided the routers maintain a table of IPv6 host routes for addresses configured from the prefixes. Routers maintain host routes through, e.g., an IPv6 routing protocol, manual configuration, etc. Hosts can learn the routes through, e.g., IPv6 ICMP redirects, manual configuration, etc. Routers can obtain IPv6 prefix delegations from a server via an ISATAP interface and advertise the delegated prefix(es) on other IPv6 interface(s). When stateful autoconfiguration is enabled, the DHCPv6 [RFC3315] server/relay function should be deployed equally on each ISATAP router. Appendix D. Site Administration Considerations ISATAP sites are administratively defined by a set of advertising interfaces and set of nodes that solicit those interfaces. Thus, ISATAP sites are defined by administrative (not physical) boundaries. Site administrators maintain a list of IPv4 addresses representing advertising ISATAP interfaces and make them available via one or more of the mechanisms described in Section 6.3.1. The list can include IPv4 anycast address(es) (e.g., for use as described in [RFC2185], section 126.96.36.199) but administrators are advised to consider operational implications of anycast (e.g., see: [RFC1546]). Responsible administration can reduce control traffic overhead associated with router and prefix discovery. Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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